Phosphor composition with self-adjusting chromaticity

ABSTRACT

Disclosed herein are “smart” phosphor compositions capable of regulating the chromaticity of their emission to substantially constant values even with variations in the excitation radiation they receive to induce photoluminescence. One phosphor of the smart composition demonstrates an increase in emission intensity increases as the wavelength of the excitation radiation is increased. The other phosphor shows a decrease in emission intensity with increasing excitation wavelength. Constant chromaticity in this context is defined as a change in CIE x or y coordinate of less than about five percent over a 10 nm range of excitation wavelengths.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a divisional of U.S. patent application Ser. No.11/805,808 filed May 23, 2007, titled Phosphor Composition withSelf-Adjusting Chromaticity, By Yi-Qun Li et al., (now U.S. Pat. No.7,820,075) which application claims the benefit of and priority to U.S.Provisional Patent Application No. 60/837,178, titled “Two-phase yellowphosphor with self-adjusting emission wavelength,” filed Aug. 10, 2006,by inventors Yi-Qun Li and Yi Dong. U.S. patent application Ser. No.11/805,808 and U.S. Provisional Patent Application No. 60/837,178 arehereby incorporated by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

Embodiments of the present invention are directed to phosphorcompositions in light emitting devices comprising a light emitting diode(LED) or laser diode and an excitable phosphor composition.

2. Description of the Related Art

The advent of GaN-based epitaxial structures has lead to the developmentof UV and/or blue (“UV/blue”) radiation sources in the form of lightemitting devices, including light emitting diodes and lasers, bothgenerally referred to herein as “LEDs.” In general, the radiation sourceexcites a phosphor or phosphor composition comprising two or morephosphors to generate visible light in the red, green, or blue region ofthe spectrum. The red, green, and blue light may then be combined tomake white light. The phosphor(s) transforms a portion of the UV and/orblue light into light of longer wavelength in a process known as downconversion. For example, a process of making white light whereby yellowlight from a phosphor such as Y₃Al₅O₁₂:Ce³⁺ (commonly referred to asYAG-Ce) is combined with the blue light from a blue LED has beendisclosed by Nichia Chemical Company.

To form white light, the YAG-Ce phosphor converts a portion of the bluelight from the blue LED chip into yellow light, which is combined withblue light from the LED that had not absorbed by the phosphor. Thisproduces a white light with a color rendering index (CRI) of about 77,and a color temperature ranging from about 6,000 to 8,000 K. For someapplications, the generation of white light by down conversion ofUV/blue light from an LED to longer-wavelength light using phosphors(and then combining light from with blue LED with light emitted by thephosphor) may be a more attractive white light to the user than whitelight made by combining red, green, and blue light directly from a red,green, and blue LED, respectively. Such UV/blue phosphor devices, forexample, enable a more widely available color range, which is importantfor display as well as for illumination applications. The addition ofdifferent phosphors to Nichia's yellow phosphor to convert UV/blue LEDlight to wavelengths other than yellow is known, and thus, it is knownthat the overall, combined color of the product light from anLED/phosphor system may be modified by adjusting the individualphosphors in a composition.

A difficulty often encountered when generating white light by thesetechniques is a variation in the quality of the white light produced asa result of statistical fluctuations that occur during the manufacturingof the blue/UV LEDs. Blue and/or UV emitting LED devices are fabricatedby depositing a variety of materials in a layered fashion onto a waferof semiconductor material. The wafer is processed to until an array oftens, hundreds, or even thousands of LEDs are made. They are thenseparated by a technique known as dicing to form the individual LED“chips.” But manufacturing LED chips in this fashion poses an inherentproblem: they cannot all be made perfectly alike, and there is bound tobe some variation among the diced LED chips. Such variations may bemanifested by color output of the LED, for example, as characterized byspectral power distribution and peak emission wavelength. Thesequantities may vary due to fluctuations in the bandgap width of theactive layer(s) of the LED(s). Another cause of variable blue/UV lightoutput is the fact that, during operation, the power supplied to used todrive the LED may fluctuate as well.

During production, a certain percentage of LEDs are manufactured withactive layers whose actual band gap width is either larger, or smaller,than that which is desired. Thus, the color output of such LEDs deviatesfrom the desired parameters. Furthermore, even if the band gap of aparticular LED does have the desired width, the power applied to the LEDcan change during operation. This can also cause the LED color output todepart from desired parameters. Since the light emitted by some systemscontains a blue component from the LED, the color output of the LEDchanges as well. A significant deviation from the desired parameters maycause the color output of the system to appear non-white (i.e., eitherbluish or yellowish).

Past solutions to this problem have included a “binning” procedure, inwhich the electroluminescent characteristics of each of the blue/UV LEDsarrayed on a wafer are measured prior to dicing, after which theindividual LEDs are categorized (or “sorted”) in terms of any of 1) peakemission wavelength of the light emitted by the LED, 2) peak intensityof the light emitted by the LED, and 3) by forward voltage. Binningrelies on the fact that LEDs are current devices. This means that theintensity of the light emitted by the LED is regulated by the electricalcurrent supplied to the LED, referred to as the “forward current.”Often, a series resistor is placed in the circuit proximal to thevoltage source: this resister protects the LED from an excessive currentoverload. The value of the forward voltage depends on this seriesresistance, the voltage supplied to the circuit, and the desired forwardcurrent through the LED (computed from the desired intensity, since thelight output is directly proportional to the forward current).

A typical commercial binning process sorts the LEDs after fabrication byany of forward voltage, peak emission wavelength, and peak emissionintensity, depending on the importance of those parameters to themanufacturer. As explained above, the voltage applied to the circuitdetermines the current that flows through the diode, which in turnaffects the intensity of the light emitted from the device. Thus,variations in portions of the circuit supporting the LED, particularlythat portion which supplies power, is manifested in the “seriesresistance” that affects the current delivered to active layer of theLED. As demonstrated schematically in FIG. 1, an imaginary wafer hasbeen diced to separate the individual LED circuits, and sorted accordingto three forward voltage groupings described generally as VF1, VF2, andVF3.

The band gap width of the LEDs' junction region determines the peakemission wavelength of the emitted light, which in turn affects coloroutput and chromaticity. For any one value of the forward current, arange of peak emission wavelengths (e.g., color output) may be observed.This is illustrated schematically in FIG. 1. For each group of forwardvoltage values, sorting further proceeds by arranging LEDs intosubgroups based on emission wavelength. In FIG. 1, a set of five binnedpeak emission wavelengths are first grouped according to the value ofthe forward voltage across the LED; then for each of the three forwardvoltage bins, LEDs are further categorized by peak emission wavelength.In the example of FIG. 1, the peak wavelength bins are centered at452.5, 455.0, 457.5, 460.0, and 462.5 nm, respectively. The binsthemselves may have the ranges: less than 450 nm, 450 to 425.5 nm, 425.5to 455 nm, 455 to 457.5 nm, 457.5 to 460 nm, and greater than 460 nm.

Some manufacturing operations may require further refinement in LEDsorting. For example, each of those bins described in FIG. 1 (which are2.5 nm wide) may be divided into an additional five bins according tochromaticity, resulting in a total now of 75 bins. The binning processcould go on indefinitely. For example, the 75 bins each having a 2.5 nmwidth may be further divided into three groups by brightness. In theexample of FIG. 1, there are now a total of 225 bins defined for all ofthe LED chips originally fabricated on the hypothetical wafer.

While desirable in some instances, binning does not have to bepredicated on wavelength ranges of the excitation source. In someprocesses, each LED chip (or “die”) is electrically connected to anexternal circuit via two electrodes, and the diced LED wafer is thentested for forward voltage of the device, or light output power from theillumination system. Exemplary categories for binning by forward voltageinto four bins are less than 3 volts, 3.0 to 3.2 volts, 3.2 to 3.4volts, and 3.4 to 3.6 volts. Alternatively, when binning is based onlight output power, such bin categories may be arranged as less than 8mW, 8 to 10 mW, 10 to 12 mW, and 12 to 14 mW.

The light output of the blue/UV LED determines in part the color outputof the illumination system (meaning LED plus phosphor). The colorcoordinate index (CIE) for a white LED produced by a blue GaN basedlight emitting diode (LED) providing excitation radiation to a yellowphosphor is controlled mainly by the emission wavelength of the lightfrom the blue LED. Thus, there is a matching process involved withpairing individual LED chips with phosphors. Thus far in the industry,it may be said in general that yellow phosphors having emissionwavelengths ranging from about 550 nm to about 575 nm have been selectedto match blue LED wavelengths ranging from about 450 nm to about 470 nm,respectively. Such matching has achieved a desired color coordinateindex, for example, of CIE (0.300, 0.300). But a large bin/sortingoperation is necessary to process today's blue LED chip output intowhite LED-based lighting systems, largely in part because of thevariation in emitting light wavelength from the blue/UV chip.

What is needed in the art is a phosphor composition designed with theability to correct, or “self-adjust” the chromaticity of the light itemits in response to wavelength/energy variations in the excitationradiation.

SUMMARY OF THE INVENTION

Disclosed herein are “smart” phosphor compositions capable ofself-adjusting their chromaticity in response to variations in theexcitation wavelengths of the blue/UV LED chips with whom they arepartnered. The illumination product formed combining the light emittedby the phosphor composition with the light emitted by the library ofblue/UV LED chips has a substantially constant chromaticity. The term“constant chromaticity” in this context means that the x and y CIEchromaticity coordinates of the product illumination each vary by nomore than five percent of a reference value.

A “smart” phosphor composition may be defined as a combination of afirst phosphor whose emission intensity decreases as the wavelength ofthe radiation being used to cause its luminescence is increased, with asecond phosphor whose emission intensity increases as the excitationwavelength is increased. The advantages of such a phosphor compositioninclude the realization of a lighting scheme that demonstratessubstantially constant chromaticity under conditions of varyingexcitation wavelength. Such a variation in wavelength of the lightemitted from different blue LED chips comes about predominantly as aresult of manufacturing variations that occurred during production ofthe blue LED chips. Manufacturing variations can lead to batches of blueLED chips having a range of band gap widths, the consequence tocommercial operations being a binning requirement, an exemplary protocoldescribed earlier in this disclosure.

Embodiments of the present invention are directed to a phosphorcomposition with self-adjusting chromaticity, the composition comprisinga first phosphor configured such that its emission intensity increaseswith increasing excitation wavelength; and a second phosphor configuredsuch that its emission intensity decreases with increasing excitationwavelength. The variation in the chromaticity of the photoluminescenceemitted by the phosphor composition is no more than about 5 percent overan about 10 nm range of excitation wavelengths. The 10 nm range ofexcitation wavelengths may extend from about 450 to about 460 nm.

In one embodiment of the present invention, the first phosphor is asilicate-based orange phosphor having the generalized formulaM₃SiO₅:Eu²⁺ where M is Sr, Ba, Mg, or Ca. Specific examples of asilicate-based orange phosphor are Sr₃Eu_(0.06)Si_(1.02)O₅(F,Cl)_(0.18),Sr_(2.94)Ba_(0.06)Eu_(0.06)Si_(1.02)O₅(F,Cl)_(0.18), and(Sr_(0.9)Ba_(0.1))_(2.76)Eu_(0.06)Si_(1.02)O₅(F,Cl)_(0.18).

In this embodiment the second phosphor may be a silicate-based greenphosphor having the generalized formula M₂SiO₄:Eu²⁺, where M is Sr, Ba,Mg, or Ca. Specific examples of the second phosphor areSr_(0.925)Ba_(1.025)Mg_(0.05)Eu_(0.06)Si_(1.03)O₄(F,Cl)_(0.12),Sr_(1.025)Ba_(0.925)Mg_(0.05)Eu_(0.06)Si_(1.03)O₄(F,Cl)_(0.12), andSr_(1.125)Ba_(0.825)Mg_(0.05)Eu_(0.06)Si_(1.03)O₄(F,Cl)_(0.12).

The use of fluorine (F) and chlorine (Cl) halogen dopants isinterchangeable in these compositions, as the choice of halogen haslittle or no relevance to the self-regulating properties of the phosphorcomposition.

According to the present embodiments, white LED-based illuminationsystems comprise a self-adjusting smart phosphor composition matched toa wide array of blue/UV emitting sources; a wider array than would havebeen possible with conventional phosphor packages. An example of a 5 nmrange in excitation is from 452.5 nm to 457.5 nm, where the desiredchromaticity of the illumination system may be maintained within thenarrow range of x±0.01 and y±0.01. The variation of the productillumination on a CIE diagram would vary from about 0.300±0.01 for the xvalue, and the 0.300±0.01 for the y value. Presently, at least 5 binsfor every 2.5 nm variation in blue/UV excitation wavelength is requiredto sort those blue LED chips; and after that, another at least 5 bins in5 different defined CIE regions would be required to satisfy presentwhite LED needs. Current methods require that in each bin brightness andvoltage have to be sorted, so at the end the LED packaging company has168 bins.

In another embodiment a white LED wafer can be manufactured by coatingthe novel smart phosphor onto a blue/UV LED wafer containing an array(which may be thousands or more) of blue/UV LED chips whose peakemitting wavelength range is larger than 5 nm (again, using theexemplary range 452.5 nm to 457.5 nm). The CIE (x, y) value of anindividual white LED chip produced from such a wafer may be controlledto within in a range of x±0.01 and y±0.01), again in the region of theCIE diagram of 0.300±0.01 for x and 0.300±0.01 for y. It is contemplatedthat the present technologies are applicable to situations where thevariation in blue/UV is more than about 5 nm across the wafer, such asthe 10 nm variation present in the industry today.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic of a sorting process by forward voltage,brightness and excitation wavelength, wherein the blue LED chips dicedfrom the as-deposited wafer are “binned,” or categorized into differentbins by spectral output, the bins then matched to a phosphor and binnedonce again, this time by CIE regions of the white light output; each CIEbin is then sorted by brightness, resulting in a total of 225 bins;

FIG. 2 is an emission spectra of two individual phosphors of anexemplary phosphor composition according to the present embodiments; inthe graph is a) the emission of a green-emitting silicate-based phosphorexcited by a blue LED excitation at peak emission wavelengths of 450 nm,455 nm, and 460 nm; b) the emission spectra of an orange emitting,silicate-based phosphor excited by the same three peak emissionwavelengths; and c) the emission spectra of a self-adjusting,two-component silicate-based phosphor composition comprising both thegreen and orange phosphors;

FIG. 3 is a CIE diagram showing the positions of the blue light emittedfrom three different blue LEDs with peak emission wavelengths at 450,455, and 460 nm, as well as the three positions of the light emittedfrom the green/orange “smart phosphor” composition when the smartphosphor composition is excited by that 450, 455, and 460 nm light; thepresent embodiments are based on the unexpected observation that thethree lines formed by connecting the 450 nm data, the 455 nm data, andthe 460 nm data each pass through the same CIE target point (in thiscase having the coordinates x=0.300 and y=0.300);

FIGS. 4A and 4B are graphs of CIE chromaticity coordinate (x and y,respectively) plotted against excitation wavelengths that range from 452to 462, the data showing that CIE coordinates for the exemplary smartphosphor composition(0.8)Sr_(1.025)Ba_(0.925)Mg_(0.05)Eu_(0.06)Si_(1.03)O₄(F,Cl)_(0.12) and(0.2)Sr_(2.94)Ba_(0.06)Eu_(0.06)Si_(1.02)O₅(F,Cl)_(0.18), aresubstantially constant within this wavelength range, varying by no morethan about one percent in either coordinate, whereas the yellow phosphorSr_(1.5)Ba_(0.45)Mg_(0.05)Eu_(0.06)Si_(1.03)O₄(F,Cl)_(0.12) shows a fourpercent change in x and eight percent change in y;

FIG. 5A is a chart giving the predominant color of emission for avariety of phosphors, and further classifies those phosphors into agroup where emission intensity increases with increasing excitationwavelength, and a group where emission intensity decreases withincreasing excitation wavelength (and one case where both increasing,neutral, and decreasing behavior was demonstrated);

FIG. 5B is a chart with the same list of phosphors arranged in columnsas well as rows, such that phosphor pairs that demonstrate the propertyof a substantially constant chromaticity even with variations inexcitation wavelength, which may also be described as a phosphor pair(or composition) that is able to self-adjust the chromaticity of itsemission even as excitation wavelength varies as a result of blue/UVchip fabrication variations;

FIGS. 6A and 6B are collections of excitation spectra of three exemplarysilicate-based green phosphors of the type M₂SiO₄:Eu²⁺ (FIG. 6A), andthree orange phosphors of the form M₃SiO₅:Eu²⁺ (FIG. 6B) over thewavelength ranges 400 to 500 nm (FIG. 6A), and 400 to about 570 nm (FIG.6B);

FIGS. 7A and 7B are collections of excitation spectra of the same greenand orange phosphors of FIGS. 6A and 6B, but plotted over an excitationwavelength range of 440 to 470 nm to show that an exemplary phosphorfrom a so-called “group A phosphor” shows an increase of 15 percent inemission intensity, whereas a representative of a “group B phosphor”demonstrates a decrease of 25 percent over the same wavelength range;and

FIG. 8 is an excitation spectrum of the commercially available phosphorsGP-4, YAG, and TAG.

DETAILED DESCRIPTION OF THE INVENTION

Disclosed herein are “smart” phosphor compositions capable of passivelyadjusting their own chromaticity (hence the term, “self-adjusting”) inresponse to variations in the excitation wavelengths of the blue/UV LEDchips with whom they are partnered. The illumination product formed bycombining the light emitted by the phosphor composition with the variouslight emitted by a library or selection of blue/UV LED chips has asubstantially constant chromaticity. The term “constant chromaticity” inthis context means that the x and y CIE chromaticity coordinates of theproduct illumination each vary by no more than five percent of areference value.

General Operating Principles

The principles of operation of a “smart” phosphor composition may beillustrated by inspecting the data in FIGS. 2 and 3. FIG. 2 is anemission spectrum of an exemplary smart phosphor composition; plottedalong with its two component phosphors, one labeled “green” and theother “orange.” The composition is “green+orange.” One will observe thatthe peak emission wavelength of the composition lies in a somewhatintermediate position to that of the individual green and orangecomponents. It will be understood that the terms “green” and “orange”are used to indicate higher and lower energies relative to yellow,regardless of the phosphors actual colors. On the left side of FIG. 2are three tall, narrow peaks that represent the three wavelengths atwhich each of the three samples were excited; these peaks are centeredat 450, 455, and 460 nm.

The data in FIG. 2 shows that as the wavelength of the excitationradiation to the green phosphor is increased from 450 to 460 nm, in fivenm increments, the intensity of the light emitted by the green phosphordecreases accordingly. Alternatively, as the wavelength of the lightused to excite the orange phosphor is increased from 450 to 460 nm, theintensity of the light emitted by the orange phosphor increasesaccordingly. An unexpected yet favorable consequence is what happens tothe resultant combination of the orange and green light: the combinedemission not only increases in wavelength with increasing wavelength ofthe excitation radiation, but the intensity of the combined emittedlight increases as well.

While not wishing to be bound by any particular theory, the observedbehavior of the individual green and orange phosphors may be explainedby the nature of the match between the energy of a photon from theexcitation light and the electrical band gap of the phosphor; the“quality” of the match being related to the efficiency at which thephosphor emits light. The light emitted by a green phosphor has a higherenergy and a shorter wavelength relative to that emitted by an orangephosphor, indicating that the green phosphor has a larger band gap.Thus, as the peak excitation wavelength is increased the energy of thisexcitation radiation decreases, becoming less and less optimally matchedto the large band gap of the green phosphor (relative to orange), andthe intensity of the emission decreases. In contrast, the orangephosphor's band gap is smaller than the green phosphor, such that as theexcitation wavelength is increased the energy of the photons decrease,and the excitation becomes better and better matched to the smaller bandgap (relative to green) of the orange phosphor. The efficiency at whichthe orange phosphor emits increases as the wavelength of the blue LEDlight is increased, indicating that the orange phosphor's lower band gapis more appropriately matched to lower energy excitation.

A “smart” phosphor composition may be defined as a combination of afirst phosphor whose emission intensity decreases as the wavelength ofthe radiation being used to cause its luminescence is increased, with asecond phosphor whose emission intensity increases as the excitationwavelength is increased. The advantages of such a phosphor compositioninclude the realization of a lighting scheme that demonstratessubstantially constant chromaticity under conditions of varyingexcitation wavelength. Such a variation in wavelength of the lightemitted from different blue LED chips comes about predominantly as aresult of manufacturing variations that occurred during production ofthe blue LED chips. Manufacturing variations can lead to batches of blueLED chips having a range of band gap widths, the consequence tocommercial operations being a binning requirement, an exemplary protocoldescribed earlier in this disclosure.

Returning to again to FIG. 2, where these concepts are illustrated withspecific data, one may observe an emission spectra of two individualphosphors of an exemplary smart phosphor composition. In the graph is:a) the emission of a green-emitting silicate-based phosphor excited by ablue LED excitation at peak emission wavelengths of 450 nm, 455 nm, and460 nm; b) the emission spectra of an orange emitting, silicate-basedphosphor excited by the same three peak emission wavelengths; and c) theemission spectra of a two-component silicate-based smart phosphorcomposition comprising the individual green and orange phosphors.Photoluminescence in the two-component composition was induced in thesame manner as it had been for the two individual green and orangephosphors; namely, at 450, 455, and 460 nm.

Referring to FIG. 2, the green phosphor was seen to decrease inintensity by at least 10 percent as the excitation wavelength wasincreased from 450 to 460 nm, where the peak emission wavelength of thegreen light emission was centered at about 530 to 540 nm. In contrast,the orange phosphor was seen to increase in intensity by at least 10percent as the excitation wavelength was likewise varied. The compositelight demonstrated an increase in the emission intensity by about fivepercent with an increase in excitation wavelength, centered in theyellow-orange at about 580 nm, even though the green phosphor is moreintense than the orange.

Advantages of the present embodiments are perhaps better appreciatedwhen data is viewed graphically on a CIE chromaticity diagram. Shown inFIG. 3, are the chromaticity coordinates plotted for the blue lightemitted from three different blue/UV LEDs having different band gapwidths, manifested by peak wavelengths of the emitted electroluminescentlight at 450, 455, and 460 nm, respectively. Also plotted in FIG. 3 arethe x and y CIE coordinates of the light emitted from a smart phosphorexcited at 450, 455, and 460 nm.

Referring again to FIG. 3, a first line on the CIE chromaticity diagramconnects a point whose x and y coordinates correspond to 450 nm emittedlight from a blue/UV LED to a point whose coordinates lie in the yellowregion of the diagram. The point in the yellowish region of the diagramis generated by emission of light from a “green/orange” smart phosphorcomposition upon excitation by the 450 nm light from the blue chip.Similarly, a second line may be drawn connecting a point at one end ofthe line having the x and y coordinates specific to 455 nm blue light,with a point at the other end of the line representing the emission ofthe smart phosphor upon excitation by 455 nm radiation. Finally, a thirdline may be drawn connecting the coordinates of 460 nm blue light from a460 nm blue LED with the coordinates of light generated by excitation ofthe smart phosphor with 460 nm light. The present embodiments are basedon the unexpected observation that these three lines (the first lineconnecting the 450 nm data, the second line connecting the 455 nm data,and the third line connecting the 460 nm data) each pass substantiallythrough a common point on the CIE diagram, in this case a desirabletarget color having x and y coordinates (0.300, 0.300).

Significant advantages of the present embodiments are that asubstantially constant chromaticity is realized within a wide range ofphosphor compositions, even with undesirable fluctuations in theexcitation wavelength. Among the advantages of the present embodimentsis that blue/UV LED chips no longer need be “sorted” or “binned” (atleast to the extent that they were before) because the smart phosphorcomposition is able to “self-adjust” the chromaticity of its lightoutput in response to LED variability. In the example of FIG. 3, thechromaticity was substantially constant over a 10 nm change inexcitation wavelength. Since one achieves the same chromaticityspecification regardless of the excitation wavelength within the 450 to460 nm range, there would have been no need to do any further sorting ofthe blue/UV LED chips.

The capability of maintaining the chromaticity at a substantiallyconstant value is important because the locus of chromaticitycoordinates that lie along the curved line passing through about (0.3,0.3) and about (0.45, 0.4) are said to lie along the Black Body Locus(BBL). This is a locus of points defined by Planck's equation:E(λ)=Aλ ⁻⁵/(e ^((B/T))−1).Here, E is the emission intensity of the phosphor composition, λ is theemission wavelength, T the color temperature of the black body, and Aand B are constants. Color coordinates that lie on or near the BBL locusof points yield pleasing white light to a human observer. Thus, as shownin FIG. 3, a composition may be designed whose color coordinates remainpositioned substantially overlapping or adjacent to the BBL curve. Thistrait is particularly desirable in white light illumination applicationswhere the optical performance of the blue/UV chips may vary overconsiderable ranges.

Further demonstration of the ability of the present compositions toself-adjust chromaticity; thereby maintaining chromaticity atsubstantially constant values even under variations of the excitationwavelength, is shown in FIGS. 4A and 4B. FIG. 4A is a plot of the CIE“x” coordinate versus excitation wavelength (varied from 452 to 462 nm),for two different phosphors labeled “SMP” and “Yellow Phosphor.” Theyellow phosphor tested had the formulaSr_(1.5)Ba_(0.45)Mg_(0.05)Eu_(0.06)Si_(1.03)O₄(F,Cl)_(0.12). Theexemplary smart phosphor (SMP) tested here was a blend of two phosphorcomponents having the formulas(0.8)Sr_(1.025)Ba_(0.925)Mg_(0.05)Eu_(0.06)Si_(1.03)O₄(F,Cl)_(0.12) and(0.2)Sr_(2.94)Ba_(0.06)Eu_(0.06)Si_(1.02)O₅(F,Cl)_(0.18). In theseformulations the nomenclature “(F,Cl) is meant to indicate that Thefluorine (F) and chlorine (Cl) halogen dopants are interchangeable asfar as the property of self-adjusting chromaticity is concerned. Inother words, the choice of halogen in these compositions has little orno relevance to the self-regulating properties of the phosphorcomposition.

Examination of FIGS. 4A and 4B shows that the x chromaticity coordinatevalues for the yellow phosphor decreased from about 0.301 to 0.288, orabout four percent, whereas the y coordinate increased from about 0.297to 0.323, or about eight percent. In contrast, the x coordinate for thesmart phosphor (SMP) varied by less than one percent over the samewavelength range, increasing slightly from about 0.303 to 0.305.Similarly, the smart phosphor's y coordinate decreased only veryslightly, from about 0.294 to 0.292 which is again less than onepercent.

The Group A and Group B Components of a Smart Phosphor

In general, phosphor compositions having a self-adjusting chromaticitymay be generated by blending a phosphor from a so-called group “A,”whose members share the common trend that emission intensity decreaseswith increasing excitation wavelength, with a Group “B” phosphor whosemembers show the opposite trend: emission intensity increases as theexcitation wavelength is increased. An exemplary range of wavelengths is450 to 460 nm.

The opposing trends used to group a phosphor make sense intuitively. Theemission intensity of a phosphor is related to efficiency at which itabsorbs its excitation radiation, and this efficiency is in turn relatedto the matching of the energy between a photon from the excitationradiation, and the band gap width of the phosphor. The light from theUV/blue LED, in this case, provides the excitation radiation to thephosphor, and in one embodiment, the UV/blue LED provides excitationradiation over a wavelength range of 450 to 460 nm.

A division between group A and group B phosphors may generally be madeat a band gap energy substantially equivalent to the energy of a photonof yellow light. Thus, group A phosphors may be said to lie on thehigher energy side of the yellow phosphors, and include blue, green, andyellow-green phosphors. Group B phosphors may be said to lie on thelower energy side of the yellow phosphors, and include yellow-orange,orange, and red phosphors. In the photoluminescent process, a phosphoris “down-converting” energy absorbed from a photon of excitationradiation to a photon that is emitted from the phosphor, the energy ofthe emission related to the phosphor's band gap through which anelectronic relaxation process occurs, this energy difference being equalto the energy of the emitted photon.

Down-conversion in group A phosphors, with their larger band gaps, ismore efficient with higher energy excitation radiation, meaning shorterwavelength light. Thus, emission intensity decreases as the energy ofthe excitation is reduced (remembering that an increase in excitationwavelength from 450 to 460 nm is a decrease in energy).

In contrast, group B phosphors lie on the orange side of yellow, andemit lower energy (longer wavelength) light relative to group Aphosphors, because of their smaller band gap widths. In this case, thedown-conversion process occurs more efficiently as the phosphor isexcited by lower and lower energies, at least within a designatedwavelength range. Thus, the emission intensity of a group B phosphorincreases with increasing excitation wavelength.

Principles which may be used to design a self-adjusting phosphor areshown in FIGS. 5A and 5B. FIG. 5A is a table that classifies a selectionof exemplary phosphors by the color of the phosphors' emission (as seenby the labels on the tables four left-hand columns: green, yellow,orange, and red). Also shown in the table of FIG. 5A is acharacterization as a group A phosphor (emission intensity decreases asexcitation wavelength is increased), or as a group B phosphor (emissionintensity decreases as excitation wavelength is increased. The exemplaryphosphors being classified according to this scheme are listed in thefar left column, and include different kinds of phosphors, includingcommercially available phosphors, phosphors described in the scientificand/or patent literature, and novel phosphors belonging to the presentinventors. The four columns under “EM color” (where “EM” stands foremission) labeled green, yellow, orange, and red, refer to the color ofthe photoluminescence.

The three phosphors at the top of the far left column are labeled“G-series,” “Y-series,” and “O-series,” and refer to phosphorcompositions developed by the present inventors, each series emittingsubstantially in the green, yellow, and orange regions of the spectrum,respectively. YAG is the commonly known material yttrium aluminumgarnet, having the formula Y₃Al₅O₁₂:Ce³⁺, and the formula of the terbiumaluminum garnet TAG is Tb₃Al₅O₁₂:Ce³⁺. YAG and TAG are commerciallyavailable phosphors that emit in the yellow and orange regions of thespectrum, respectively. GP-4 is a green emitting YAG phosphor, alsocommercially available, having the formula Y₃(AlGa)₅O₁₂:Ce³⁺, and likeYAG and TAG, it too is activated by trivalent cerium.

Below those top three phosphors in the far left column are threesulfide-based phosphors, and below those, three phosphors based onsilicon nitride and silicon oxynitride. Of the sulfides, two emit in arelatively narrow spectral range, SrGa₂S₄:Eu in the green, and CaS:Eu inthe red. The silicon nitride and silicon oxynitrides are also capable ofemitting over a relatively large spectral range, with SrSi₂O₂N₂:Euemitting in the green and yellow, and (Sr,Ba,Ca)₂Si₅N₈:Eu emitting inthe yellow, orange, and red, when compositional changes are made in therelative amounts of the alkaline earth components. In at least one casewhere the alkaline earth component was fixed using a single element, thephosphor emitted in a more narrow range of the spectrum, primarilywithin a single color range. For example, the silicon nitride basedphosphor Si₂Si₅N₈:Eu emitted in the red.

Referring again to FIG. 5A, the three columns on the far right hand sideof the table headed by the label “EX Curve (450 to 460 nm)” are furtheridentified by the three conditions: 1) an arrow slanting upwards and tothe right, 2) a horizontal line, and 3) an arrow slanting downwards andto the right. These labels refer to whether a particular phosphorshow: 1) an increase in emission intensity, 2) no change in intensity,or 3) a decrease in intensity, respectively, as the excitationwavelength is increased within the range 450 to 460 nm. For example, theshaded box in the top row of FIG. 5A under the decreasing arrow meansthat the G-series phosphor demonstrates a decrease in emission intensityas the excitation wavelength is increased. In contrast, the shaded boxin the third row down says that O-series phosphor exhibits an increasein emission intensity as the wavelength of the excitation radiation isincreased. It is this behavior that classifies a phosphor into eithergroup A or group B according to the present embodiments.

While the trends demonstrated by the orange and green phosphors of FIG.5A are somewhat predictable, what is not readily apparent is thebehavior of a yellow phosphor. One might expect a yellow phosphor toexhibit a pattern intermediate to that of group A and group B; that is,to show no change in emission intensity with increasing excitationwavelength. This scenario might be expected because of a somewhat lessersensitivity of a yellow phosphor to variations in excitation energy,since these yellow phosphors have band gap energies that areintermediate in a range defined by all the photoluminescent phosphorsthat emit in the visible. But this is not the case as the yellowphosphors sometimes fall into the group A category, sometimes into thegroup B category, and sometimes the behavior appears to be too complexto be categorized.

Examples of the yellow phosphors that may be categorized as group Bphosphors are the Y-series developed by the present inventors (althoughthese may more accurately be described as “yellow-green,” as describedbelow), and the silicon oxynitride SrSi₂O₂N₂:Eu. One example of aphosphor falling into group A is the highly conventional andcommercially available, Ce doped phosphor yellow-YAG; another is thesilicon nitride compound (Sr,Ba,Ca)₂Si₅N₈:Eu. The former observation maysuggest that the yellow YAG may more accurately be thought of as ayellow-orange phosphor, whereas the output of the silicon nitride may beadjusted via the ratio of the alkaline earth elements.

A benchmark against which other group A/group B pairs may be judged,particularly in terms of the ability to self-regulate chromaticity, isthe composition made by combining a “G-series” phosphor of the typeM₂SiO₄, with an “O-series” phosphor of the type M₃SiO₅, where M is analkaline earth element in both types of silicates, and where phosphorsof the G and O-series were developed by the present inventors. TheG-series phosphors may also be used in combination with a Y-series ofphosphors, again belonging to the present inventors, where phosphors inthe Y-series have the M₂SiO₄ configuration. Though the latter arerepresented in FIG. 5A as emitting in the yellow, previously fileddisclosures on these compounds provide experimental data showing them tobe more “yellow-green” than yellow, the higher energy green contributiongiving them their group B classification. Another example of a smartpair is given by a G or Y-series phosphor with a conventional ceriumdoped yellow YAG phosphor, remembering that the latter behaves as agroup A phosphor and thus may be thought of as “yellow-orange.” Yetanother smart phosphor is suggested by the combination of a group B (Gor Y-series) phosphor with an orange TAG phosphor, and this indeed hasproven to be correct.

As alluded to previously, not all combinations of a group A phosphor anda group B successfully produce the constant chromaticity property. Anexample of a group A phosphor paired with a group B phosphor whichcombination does not produce any significant “smart activity” are thecommercially available green YAG (also denoted as GP-4) and the ceriumdoped yellow YAG phosphor, shown as an unshaded cell in FIG. 5B in thecolumn headed by “YAG” and the row labeled “GP-4 (Green YAG).”

Group A and B Behavior Contrasted by Excitation Spectra

That the group A and group B phosphors of the present invention havecontrasting behavior with regard to their excitation spectra is furtherillustrated in FIGS. 6A, 6B, 7A, and 7B. FIGS. 6A and 6B are excitationspectra measured at between 400 and 500 nm, where the green phosphorsG525, G530, and G535 show a decrease in emission intensity withincreasing excitation wavelength, particularly from about thewavelengths 450 to 500 nm. In contrast, the emission intensity of theorange series of phosphors O5446, O5544, and O5742 generally increase asthe excitation increases from about 450 nm to about 520 to 540 nm. Atwavelengths longer than 540 nm, even the orange series of phosphorsdecrease in emission intensity with increasing excitation wavelength.The compositions of these exemplary oranges phosphors used to producethe excitation curves FIGS. 6A, 6B, 7A, and 7B are:Sr₃Eu_(0.06)Si_(1.02)O₅(F,Cl)_(0.18) for O5446;Sr_(2.94)Ba_(0.06)Eu_(0.06)Si_(1.02)O₅(F,Cl)_(0.18) for O5544, and(Sr_(0.9)Ba_(0.1))_(2.76)Eu_(0.06)Si_(1.02)O₅(F,Cl)_(0.18) for O5742.Again, the nomenclature “(F,Cl)” means that these halogens areinterchangeable.

Further quantification of the behavior of group A and group B phosphorsis shown in FIGS. 7A and 7B. This set of data shows that the set oforange type phosphors specifically identified by the labels O5742,O5746, and O5544 increases in emission intensity as the excitationwavelength is increased from 440 to 470 nm, within the blue region ofthe blue/UV excitation source. This represents about an increase in 15percent in emission intensity. On the other hand, the green typephosphors G530, G535, and G525 decrease in emission intensity by about25 percent, as illustrated in FIG. 7B.

Excitation spectra of the commercially available phosphors YAG, TAG, andGP-4 are given in FIG. 8.

Specific Examples of Smart Phosphor Pairs

In addition to the benchmark of smart phosphor performance given by thepresent inventors' G and O-series phosphors, examples will be providednow utilizing at least one commercially available and/or prior artcomponent phosphors. The results from testing pairs of phosphors aresummarized in FIG. 5B, where cell shading indicates that that particularcombination of phosphors exhibits at least some degree ofself-regulating ability. In one embodiment of the present invention, asmart phosphor comprises a group B, green YAG phosphor with a group A,orange TAG phosphor. The present inventors' group B, Y-series phosphormay also be combined with the group A, orange TAG phosphor.

In another embodiment, a smart phosphor comprises a group B, greenSrGa₂S₄:Eu phosphor and a group A, O-series phosphor invented andpreviously disclosed by the present inventors. The green SrGa₂S₄:Euphosphor may also be combined with either a group A, yellow YAG or anorange TAG phosphor.

In another embodiment of the present invention, a smart phosphor is madeby combining a group A, red CaS:Eu phosphor with a phosphor from eitherof the G or Y-series of green and yellow-green, silicate-based phosphorsprovided by the present inventors. The red CaS:Eu may also be combinedwith other group B phosphors, such as the GP-4 green YAG and the greenSrGa₂S₄:Eu phosphors.

Turning now to the silicon oxynitrides, the group B, green (and/oryellow) SrSi₂O₂N₂:Eu compound may in one embodiment be combined with anyof the group A phosphors selected from the group consisting of thepresent inventors' O-series, silicate-based phosphors previouslydisclosed, a yellow (possibly yellow-orange) YAG, an orange TAG, and ared CaS:Eu phosphor.

A number of smart phosphor compositions may be designed around thesilicon nitride compound (Sr,Ba,Ca)₂Si₅N₈:Eu. The relative content ofthe alkaline earth elements in this compound may be varied to constructa “family” of phosphors emitting either a green, yellow, orange, or redcolor, as desired. Accordingly, the green and yellow emitting versionsof this phosphor demonstrate group B behavior; the orange and redversion group A behavior. Each member of the series may be identified byit emission color: (Sr,Ba,Ca)₂Si₅N₈:Eu, yellow (Sr,Ba,Ca)₂Si₅N₈:Eu,orange (Sr,Ba,Ca)₂Si₅N₈:Eu, red (Sr,Ba,Ca)₂Si₅N₈:Eu phosphor, and thelike.

In some embodiments of the present invention, a smart phosphor comprisesa group B, green and/or yellow (Sr,Ba,Ca)₂Si₅N₈:Eu silicon nitridephosphor with a group A, Y-series or O-series, silicate-based phosphorpreviously disclosed by the present inventors. Alternatively, the greenand/or yellow (Sr,Ba,Ca)₂Si₅N₈:Eu phosphor may be paired with a group A,yellow YAG or orange TAG phosphor. It may also be paired with the redsulfide CaS:Eu.

Common to phosphor compositions that may be configured to emit over awide spectral range is the ability to pair a green or yellow version ofthe phosphor with an orange or red version of the same phosphor, and thesilicon nitride family (Sr,Ba,Ca)₂Si₅N₈:Eu is advantageously used inthis situation as well. In this embodiment, a group B, green or yellow(Sr,Ba,Ca)₂Si₅N₈:Eu phosphor is paired with a with a group A, orange orred (Sr,Ba,Ca)₂Si₅N₈:Eu phosphor, such that the majority of thecomposition of this embodiment is (Sr,Ba,Ca)₂Si₅N₈:Eu.

Smart phosphors may also be designed around (Sr,Ba,Ca)₂Si₅N₈:Eu in itsgroup A configuration, designated by orange (Sr,Ba,Ca)₂Si₅N₈:Eu and red(Sr,Ba,Ca)₂Si₅N₈:Eu. In one embodiment of the present invention, a smartphosphor is made by combining a group A, red (Sr,Ba,Ca)₂Si₅N₈:Eu with agroup B phosphor selected from the group consisting of a G-seriessilicate-based phosphor, a Y-series silicate-based phosphor, and a greenSrSi₂O₂N₂:Eu phosphor.

G-Series and Y-Series Silicate-Based Phosphor Compositions

More general descriptions of the G-series and Y-series phosphors of thepresent embodiments will now be given. Phosphors of the G-seriescomprise silicate-based compounds having the formula M₂SiO₄:Eu²⁺, whereM is Sr, Ba, Mg, or Ca.

As taught by G. Blasse et al. in Philips Research Reports Vol. 23, No.1, pp. 1-120, the crystal structure of a β-Ca₂SiO₄:Eu, Sr₂SiO₄:Eu, orBa₂SiO₄:Eu composition, with Eu²⁺ at a concentration of 2 atomicpercent, is K₂SO₄-like. Thus, it is contemplated that the presentG-series green silicate phosphors have a similar host lattice.

The optical properties of these G-series phosphors may be controlled,among other methods, by adjusting the ratio of the alkaline earth cationto strontium. For example, the wavelength position at which the peakemission occurs changes in a (Sr_(1-x)Ba_(x))₂SiO₄ phosphor system froma green at 500 nm for x=1 (in other words, when the alkali metal contentis 100 percent Ba) to a yellow at 580 nm when x=0 (100 percent Sr). Theconversion efficiency from the same light source at 450 nm shows acontinuous increase when the Ba increases from 0 to about 90 percent.The peak emission wavelength of 545 nm, obtained when x=0.3, is close tothat of a YAG:Ce peak emission wavelength.

There are a variety of ways to include the halogen anion into theinventors' own G-series, green silicate-based phosphors. In oneembodiment, a halogen is added to the phosphor composition during aliquid phase step of processing, such as that encountered during thesol-gel or co-precipitation processing methods. This liquid processingallows for mixing on a molecular level, such that the halogen anion iswell dispersed within the composition prior to later crystallizationsteps (e.g., sintering). The present inventors have previously foundthat the halogen anion influences both emission intensity and peakwavelength. While not wishing to be bound by any particular theory, itis believed that the luminescence of these phosphors Eu dopedsilicate-based phosphors is due to of the Eu doped phosphors is due anelectronic transition from 4f⁶5d¹ to 4f⁷ in the Eu²⁺ activator. Emissionwavelength depends on the crystal field splitting of the 5d level. Withincreasing crystal field strength, emission wavelengths increase. Theluminescence peak energy of the 5d to 4f transition is affected the mostby parameters that affect electron-electron repulsion in the crystal; inother words, the distance between Eu²⁺ cations and its surroundinganions, and the average distance between cations and ions.

Liquid processing enables at least some of the halogen anions to replacethe O²⁻ anions of the host silicate, and to become incorporated into thecrystal lattice. As the halogen anion is monovalent, then cationvacancies may be created in the crystal lattice in order to maintainelectrical charge neutrality. Since vacancies at the cation positionsreduce the average distance between cations and anions, the crystalfield strength will be increased. Therefore, the peak of the emissioncurves will move to longer wavelengths as the halogen content increases,and as more cation vacancies are created. The emission wavelength isdirectly related to the energy gap between the ground and excited statesof the electron in question, and this in turn is determined by thecrystal field strength.

In the case of the present silicate-based phosphors, the fact thatemission wavelength increases as a function of increasing halogencontent (within a certain range of halogen content) is strong evidenceof halogen incorporation into the host lattice, most likelysubstitutionally located on oxygen lattice sites. In one embodiment ofthe present invention, the halogen anion is fluorine or chlorine.Additional evidence of halogen incorporation into the lattice isprovided by the data when phosphorus (P) is added to the composition,phosphorus being a cation in at least the case of the G-seriesphosphors. Addition of phosphorus does not substantially change emissionwavelength, and this is evidence, again, that the phosphorus behaves asa cation and therefore does not replace oxygen in the host crystal.Thus, phosphor addition does not appreciably change the host material'scrystal field strength in the crystal field surrounding the Eu²⁺ ions,which consist essentially of oxygen sites.

Phosphors of the O-series comprise silicate-based compounds having thegeneralized formula M₃SiO₅:Eu²⁺, where M is an divalent cation such asmagnesium (Mg), calcium (Ca), barium (Ba), strontium (Sr), or zinc (Zn).The phosphors may also contain the halogens fluorine (F), chlorine (Cl),and/or bromine (Br).

An exemplary Y-series phosphor configured to emit light having awavelength ranging from about 460 to 590 nm has the composition(Sr_(1-x-y)Ba_(x)Ca_(y)Eu_(0.02))₂SiO_(4-z)D_(z), where 0<x≦1.0,0<y≦0.8, and 0<z≦0.2. An alternative formula for an exemplary Y-seriesphosphor is (Sr_(1-x-y)Ba_(x)Mg_(y)Eu_(0.02))₂SiO_(4-z)D_(z), where0<x≦1.0, 0<y≦0.2, and 0<z≦0.2. In an alternative embodiment the Y-seriesphosphor is (Sr_(1-x-y)Ba_(x)M_(y)Eu_(0.02))₂SiO_(4-z)D_(z), where0<x≦1.0, and M is one or more of Ca, Mg, An, and Cd. In this embodiment,the condition 0<y≦0.5 applies when M is Ca; 0<y≦1.0 when M is Mg, and0<z≦0.5 when M is either Zn or Cd. In one embodiment, the dopant D iseither F, or Cl, or both, and in this embodiment, at least some of the For Cl replaces oxygen in the host crystal lattice.

O-Series Silicate-Based Phosphor Compositions

Phosphors of the O-series comprise silicate-based compounds having theformula (Sr,A₁)_(x)(Si,A₂)(O,A₃)_(2+x):Eu²⁺, where A₁ is at least onedivalent cation (a 2+ ion) including magnesium (Mg), calcium (Ca),barium (Ba), or zinc (Zn), or a combination of 1+ and 3+ cations, A₂ isa 3+, 4+, or 5+ cation, including at least one of boron (B), aluminum(Al), gallium (Ga), carbon (C), germanium (Ge), and phosphorus (P); andA₃ is a 1−, 2−, or 3− anion, including fluorine (F), chlorine (Cl),bromine (Br); and x is any value between 2.5 and 3.5, inclusive. As withthe G-series phosphors, the formula for the Y-series phosphors iswritten to indicate that the A₁ cation replaces silicon (Si), and the A₃anion replaces oxygen (O).

Phosphors of these O-series, silicate-based phosphors may also bedescribed in general by the formula (Sr_(1-x)M_(x))_(y)Eu_(z)SiO₅,wherein M is at least one of a divalent alkaline earth metal selectedfrom the group consisting of Ba, Mg, and Ca, but it may include otherdivalent elements as well, such as Zn. The values of x, y, and z followthe following relationships: 0<x≦0.5, 2.6<y<3.3, and 0.001<z≦0.5. Thephosphor is configured to emit light having a wavelength greater thanabout 565 nm. In some embodiments, the O-series phosphor has the formulaSr₃Eu_(z)SiO₅. In alternative embodiments the phosphor could be(Ba_(0.05)Mg_(0.05)Sr_(0.9))_(2.7)Eu_(z)SiO₅, or(Ba_(0.075)Mg_(0.025)Sr_(0.9))₃Eu_(z)SiO₅, or(Ba_(0.05)Mg_(0.05)Sr_(0.9))₃Eu_(z)SiO₅. In alternative embodiments thephosphor has the formula (Mg_(x)Sr_(1-x))_(y)Eu_(z)SiO₅,(Ca_(x)Sr_(1-x))_(y)Eu_(z)SiO₅, and (Ba_(x)Sr_(1-x))_(y)Eu_(z)SiO₅,wherein the values of x and y follow the rules 0<x≦1 and 2.6<y<3.3, andwherein the relationship between y and z is such that y+z is about equalto 3.

As taught by G. Blasse et al. in Philips Research Reports Vol. 23, No.1, pp. 1-120, the host lattice in a phosphor belonging to the systemMeSiO₅, where Me is either Ca, Sr, or Ba, has the crystal structure (oris related to the crystal structure) Cs₃CoCl₅. Thus, it is contemplatedthat the present O-series, orange silicate-based phosphors have asimilar host lattice.

To describe the desired amount of activator content, the O-seriesphosphors may be represented in general by the formula(Sr_(1-x)M_(x))_(y)Eu_(z)SiO₅, where the level of the europium activatoris described by the “z” parameter, which may range from about0.001<z<0.5. The effects of including a halogen into the O-seriesphosphors may be described by embodiments having the formula(M_(1-x)Eu_(x))_(y)SiO₅H_(6z). In this embodiment, H is a halogen anionselected from the group consisting of F, Cl, and Br, and the amount ofthe halogen included in the composition is described again by theparameter “z.” Here, z ranges from 0<z<0.1.

Self-Adjusting Smart Phosphor for Constant Chromaticity and itsImplications for Binning of a White Illumination System

According to the present embodiments, white LED-based illuminationsystems comprise a self-adjusting smart phosphor composition matched toa wide array of blue/UV emitting sources; a wider array than would havebeen possible with conventional phosphor packages. An example of a 5 nmrange in excitation is from 452.5 nm to 457.5 nm, where the desiredchromaticity of the illumination system may be maintained within thenarrow range of x±0.01 and y±0.01. The variation of the productillumination on a CIE diagram would vary from about 0.300±0.01 for the xvalue, and the 0.300±0.01 for the y value. Presently, at least 5 binsfor every 2.5 nm variation in blue/UV excitation wavelength is requiredto sort those blue LED chips; and after that, another at least 5 bins in5 different defined CIE regions would be required to satisfy presentwhite LED needs. Current methods require that in each bin brightness andvoltage have to be sorted, so at the end the LED packaging company has168 bins.

In another embodiment a white LED wafer can be manufactured by coatingthe novel smart phosphor onto a blue/UV LED wafer containing an array(which may be thousands or more) of blue/UV LED chips whose peakemitting wavelength range is larger than 5 nm (again, using theexemplary range 452.5 nm to 457.5 nm). The CIE (x, y) value of anindividual white LED chip produced from such a wafer may be controlledto within in a range of x±0.01 and y±0.01), again in the region of theCIE diagram of 0.300±0.01 for x and 0.300±0.01 for y. It is contemplatedthat the present technologies are applicable to situations where thevariation in blue/UV is more than about 5 nm across the wafer, such asthe 10 nm variation present in the industry today.

What is claimed is:
 1. A process to produce an illumination system comprising: providing a plurality of blue LEDs wherein said plurality of blue LEDs have peak emission intensities at wavelengths over a range of greater than or equal to 5 nm; and coating said plurality of blue LEDs with a phosphor composition comprising two phosphor materials, such that each of the CIE(x,y) color coordinates of each of the coated blue LEDs are within a range of x of ±0.01 and a range of y of ±0.01.
 2. The process of claim 1, wherein a first phosphor material of said phosphor composition is configured to emit yellow light with a peak emission intensity wavelength that increases with increasing excitation wavelength, and a second phosphor material of said phosphor composition is configured to emit yellow light with a peak emission intensity wavelength that decreases with increasing excitation wavelength.
 3. The process of claim 1, wherein a first phosphor material of said phosphor composition has a shorter peak emission intensity wavelength than a second phosphor material of said phosphor composition; wherein the peak emission intensity of said first phosphor material decreases as the excitation wavelength is increased; and wherein the peak emission intensity of said second phosphor material increases as the excitation wavelength is increased.
 4. The process of claim 1, wherein a first phosphor material of said phosphor composition has a shorter peak emission intensity wavelength than a second phosphor material of said phosphor composition; wherein the peak emission intensity of said first phosphor material decreases as the excitation wavelength is increased; and wherein the peak emission intensity of said second phosphor material is substantially unchanged as the excitation wavelength is increased.
 5. The process of claim 1, wherein a first phosphor material of said phosphor composition has a shorter peak emission wavelength than a second phosphor material of said phosphor composition; wherein the peak emission intensity of said first phosphor material is substantially unchanged as the excitation wavelength is increased; and wherein the peak emission intensity of said second phosphor material increases as the excitation wavelength is increased.
 6. The process of claim 1, wherein said range of peak emission intensity wavelengths of said plurality of blue LEDs lies between 440 nm and 480 nm.
 7. The process of claim 1, wherein the peak emission intensity wavelengths of the light emitted from said phosphor composition range from 545 nm to 580 nm.
 8. The process of claim 1, wherein said plurality of blue LEDs are on a wafer.
 9. The process of claim 1, wherein said plurality of blue LEDs have peak emission intensities at wavelengths over a range of about 10 nm.
 10. The process of claim 1, wherein said phosphor composition includes a first phosphor material that is a silicate-based orange phosphor selected from the group consisting of Sr₃Eu_(0.06)Si_(1.02)O₅(F,Cl)_(0.18), Sr_(2.94)Ba_(0.06)Eu_(0.06)Si_(1.02)O₅(F,Cl)_(0.18), and (Sr_(0.9)Ba_(0.1))_(2.76)Eu_(0.06)Si_(1.02)O₅(F,Cl)_(0.18).
 11. The process of claim 1, wherein said phosphor composition includes a second phosphor material that is a silicate-based green phosphor selected from the group consisting of Sr_(0.925)Ba_(1.025)Mg_(0.05)Eu_(0.06)Si_(1.03)O₄(F,Cl)_(0.12), Sr_(1.025)Ba_(0.925)Mg_(0.05)Eu_(0.06)Si_(1.03)O₄(F,Cl)_(0.12), and Sr_(1.125)Ba_(0.825)Mg_(0.05)Eu_(0.06)Si_(1.03)O₄(F,Cl)_(0.12).
 12. The process of claim 1, wherein said plurality of blue LEDs have peak emission intensities at wavelengths over a range of greater than 5 nm.
 13. A process to produce an illumination system comprising: providing a plurality of blue LEDs wherein said plurality of blue LEDs have peak emission intensities at wavelengths over a range of 10 nm; and coating said plurality of blue LEDs with a phosphor composition comprising two phosphor materials such that the x values of the CIE(x,y) color coordinates of each of the coated LEDs are within a range of 5% and the y values of the CIE(x,y) color coordinates of each of the coated LEDs are within a range of 5%.
 14. The process of claim 13, wherein a first phosphor material of said phosphor composition is configured to emit yellow light with a peak emission intensity wavelength that increases with increasing excitation wavelength, and a second phosphor material of said phosphor composition is configured to emit yellow light with a peak emission intensity wavelength that decreases with increasing excitation wavelength.
 15. The process of claim 13, wherein a first phosphor material of said phosphor composition has a shorter emission wavelength than a second phosphor material of said phosphor composition; wherein the peak emission intensity of said first phosphor material decreases as the excitation wavelength is increased; and wherein the peak emission intensity of said second phosphor material increases as the excitation wavelength is increased. 